For dog lovers, it’s an absolute: The unconditional love of a canine companion heals the soul, reaching into the heart to cross canyons of loneliness and despair.

Military researchers now are trying to learn if there’s real science behind that semimystical link — and if so, whether it can help treat the signature wounds of the Iraq and Afghanistan wars.

A $5 million study is underway at the Walter Reed National Military Medical Center in Bethesda, Md., to evaluate whether and how training service dogs may help patients with traumatic brain injury or post-traumatic stress disorder.

Participating troops are paired with puppies that they will raise for two years to serve as assistance dogs for other injured veterans.

Anecdotal personal stories aside, a handful of studies have suggested that working with dogs releases oxytocin, the feel-good hormone that promotes bonding. The new research seeks to quantify these observations.

“There’s not a lot of information. ... It’s hard to conduct randomized, controlled trials as to why some people benefit,” said Navy Capt. Robert Koffman, a psychiatrist contributing to the study as part of his job at the National Intrepid Center of Excellence in Bethesda.

The research is modeled on a program started five years ago at the Veterans Affairs Palo Alto Health System in California.

Rick Yount, executive director of the nonprofit Warrior Canine Connection, which breeds golden and Labrador retrievers to become service dogs, said the program succeeds by combining the power of the human-animal bond with the “warrior ethos” of helping brothers-in-arms.

Being in need of mental health treatment is “contrary” to how combat troops see themselves, Yount said, “but tell them you need volunteers to help train service dogs, and a lot of hands go up.”

The study involves at least 40 service members, half of whom will train dogs.

The research will follow participants through the program, examining physiological responses — such as heart rate and stress markers — as well as any psychiatric changes before, during and after the study period.

If the results are anything like what Palo Alto has seen, Yount said troops will benefit, and a new crop of hard-working service dogs will be available for injured vets.

“While service members are trying to teach the dog that the world is a safe place, they are, at the same time, working on their own triggers,” Yount said.

The study is the first Defense Department research to examine the interaction between dogs and humans with head injuries or mental health conditions.

A larger, different study is just getting underway at the Veterans Affairs Department, but that research will focus on the effectiveness of trained psychiatric service dogs as well as companion dogs — pets — to ease PTSD symptoms.

On any given day, service dogs can be spotted strolling through the NICoE, Building 62, which houses injured troops, and the America Building outpatient clinics at Walter Reed-Bethesda.

Koffman’s golden-Lab mix, Ron, works as an animal assistance therapy dog, breaking the ice between his handler and patients.

He said the magnetic draw of dogs is one of many reasons they’re beneficial to patients with anxiety disorders, including PTSD.

“When you have a dog in public that’s as irresistible as mine, it’s almost impossible to get anywhere on time,” he said. “It forces a person to socialize.”

The Pentagon is expected to update Congress on the research’s progress next year. Advocates say the results may guide the military, veteran and medical communities on canine-assisted therapy, service dog policies, medical treatment and more.

Retired Army Col. Elspeth Ritchie, lifelong dog lover and chief clinical officer for the Washington, D.C., Department of Mental Health, said dog therapies “are not yet a ‘best practice.’ ... They’re still new and emerging.”

“But the anecdotal information — just from talking with the service member — is so strong,” she said. “As complementary or alternative medicine, it’s powerful.”